Currently, most motor vehicles are equipped with disk brakes, in which a metal, carbon or ceramic disk is rigidly affixed to a car wheel. To cause braking, a pair of pads, one on either side of the disk, is pressed onto the surface of the disk, causing friction and slowing the vehicle. One challenge in the design of disk brakes is the need to absorb and dissipate the great amount of heat that is generated, as the kinetic energy of the vehicle is converted to heat energy by brake friction.
In currently available disk brakes systems, the heat of braking is absorbed by the material mass between the two rubbing surfaces of each disk. This heat is dissipated, as the disk spins, through a) air convection on the two rubbing surfaces, b) air convection in ventilation passageways cast into the disk, and c) heat radiation of the two rubbing surfaces, if the surfaces become red hot. A high surface temperature reduces a brake pad's life and friction coefficient dramatically, and is therefore highly undesirable.
Another problem encountered with disk brakes is that of incomplete outer brake pad disengagement after braking. Although the inner brake pad is affirmatively withdrawn a slight distance (0.15 mm), the outer brake pad tends to gently rub against the disk, after braking. This reduces fuel efficiency.
Also, as in any automotive component, the weight of a disk brake must be carried by the vehicle, so that any reduction in weight is desirable.